The present invention relates to a proton conductor, a production method thereof, a polymer made of proton conductors, methods of making the polymer, and an electrochemical device using the polymer of proton conductors.
One of the most widely used proton conductors is Nafion, which is a perfluorinated sulfonic acid functionalized polymer. The structure of Nafion is shown in FIG. 3, and can essentially be divided in two substructures: i) a perfluorinated linear backbone 12; and ii) perfluorinated side chains 14 bearing sulfonic acid functions, i.e., the proton delivering sites. It combines an acceptable proton conductivity with an extreme inertness against chemical as well as thermal influences.
In addition, known fullerene compounds include, for example, compounds 1 through 6 (see FIGS. 4A–F) bearing acidic functional groups like sulfuric acid esters (—OSO3H) or sulfonic acid groups (—SO3H) that are capable of conducting protons within their solid-state structure. These proton-delivering sites can either be attached directly to the fullerene core or via various spacer molecules. Depending on the amount of water contained within the crystal, these compounds show proton conductivities higher than 10−2 S/cm. However, these fullerene-based materials suffer from several disadvantages. The most striking one is a lack of resistance to thermal and/or chemical decomposition. As an example, the butyl-linked fullerosulfonic acid (compound 6, FIG. 4F) first starts to decompose at about 100–110° C. Yet, thermal and chemical stability are prerequisites for any compound used in a fuel cell application.
Accordingly, there exists a need to provide materials that can be effectively and readily made and used as proton conductors for a variety of difference applications.